Rather than use food coloring, I decided to go au naturale with pureed fresh blueberries for a subtle hint of blue. (makingthymeforhealth.com)
Adelard of Bath neatly summed this up in Quaestiones naturales, with this rejoinder to his nephew: (faith.org.uk)
200 g cleaned cherries 300 g cleaned strawberries, cut into quarters the juice of half a lemon the juice of 1 orange 1 tablespoon naturale vanilla extract 2 tablespoons molasses (from whole cane sugar) the juice of 2 cm cleaned and grated fresh ginger root 4 - 5 fresh mint leaves, cleaned and chopped 1/4 teaspoon of powdered cloves (cottoecrudo.com)